Cilia are important cell organelles of organisms including man. This study continues a comprehensive attack on the structure and function of cilia, including analysis of the mechanism of movement and its regulation, primarily using electron microscope techniques. Ciliary motility is now known to be powered by a sliding microtubule mechanism, involving interaction of dynein arms with the axonemal microtubules. A mechanochemical cycle of dynein arm activity has been postulated and is being tested by a series of studies involving (1) scoring of arm attachment after specific physiological treatments of axonemes to cause reactivation or arrest and (2) dynein decoration experiments. In the intact beating cilium, the unfettered arm cycle is severely restricted and regulated, in part by Ca(II). We are examining whether the operative calcium binding protein of the axoneme is calmodulin. This information should lead to further understanding of mechanisms of normal ciliary activity, which are important contributions to human respiratory health or disease.